Liquids, e.g., water, oil and the like, are often "conditioned" by passing them through filter cartridges to remove particulate matter. It may be said that such particulate matter is removed "mechanically" by impeding particulate movement as the liquid being filtered flows through the cartridge. Such cartridges are typically confined within a housing through which the liquid flows for filtering. Some installations use multiple filter cartridges within a single housing. Examples of a filter cartridge and housing are disclosed in U.S. Pat. Nos. 3,988,244 (Brooks), 4,507,200 (Meissner) and 5,190,651 (Spencer et al.).
Another type of arrangement used to purify water in a different way, i.e., by killing bacteria in such water, involves flowing water across a catalyst. Bacteria in the water are killed upon coming into contact with such catalyst. Aspects of this technology are described in "Research Note: O.sub.3 or O.sub.2 and Ag: A New Catalyst Technology for Aqueous Phase Sanitation" published in Ozone Science & Engineering, Vol. 15, pp. 533-546, and "A Story About O" published in Pool & Spa News, May 17, 1993. The latter depicts water flowing through a container housing a catalyst.
Patent literature is also of interest. U.S. Pat. No. 4,092,245 (Franks, deceased et al.) describes a water purification system with a filter shell housing a group of filter elements. After water is pre-filtered in the shell, it is directed to a separate shell housing a catalytic filter. Such filter has a number of horizontal perforate filter plates covered with high-friction filter cloth overlayed with a fine-powder biocatalyst layer. Because such layer can migrate through the horizontal plates, the patent explains that it is a good idea to apply a base coat of diatomaceous earth (DE) to the filter cloth.
U.S. Pat. No. 5,279,748 (Hackett) discloses a pool filter providing what the patent calls "electrolytic action" using particles of dissimilar metals. Copper and zinc are mentioned.
The filter has a container, the bottom of which supports a lower layer of gravel. The loose electrolytic medium rests atop the gravel. The piping is configured in such a way that water flows "top down" through the electrolytic medium and then radially through vented laterals in each of three outlet tubes. One of the stated features of the Hackett filter is that it removes chlorine and eliminates the need for chlorine.
While these prior art arrangements seem generally suited for their intended purposes, they are not without disadvantages. For example, the arrangement described in the Pool & Spa News article contemplates either using the catalyst without a particulate filter or using such catalyst with a separate (and separately-plumbed) filter cartridge and housing. In view of the invention, the need to operate without a filter cartridge (thereby permitting most particulates to remain in the water) and the complexity and added cost attending use of a separate catalyst holder are both unnecessary.
The arrangement disclosed in the Franks et al. patent uses separate housings for the small-mesh filter elements and for the catalyst. Using the latter requires (or at least recommends) applying a base coat of DE to the filter cloth. While the invention may be used with DE, persons familiar with the filter arts involving DE are well aware of how difficult it is to apply an evenly-thick coating thereof to filter cloth.
The arrangement disclosed in the Hackett patent contemplates some type of mechanical filter but seemingly fails to appreciate certain details of water purification. It is stated that the metal particles provide "controlled releases of oxides" into the water to kill bacteria. And the electrolytic granules change bacteria-killing chlorine (which is an oxidizer) into oxides and salts. Thus, it appears that the Hackett filter kills bacteria in generally the same way that chlorine in water kills bacteria, i.e., by dispersing a chemical in the water. To put it another way, there seems to be no "kill-on-contact" action at the site of the electrolytic granules, notwithstanding that the patent mentions a "catalytic action."
And in both the Hackett and Franks et al. arrangements, the electrolytic granules and catalyst, respectively, are loose in the container. There is no way to conveniently replace such granules and catalyst.
None of the prior art arrangements mentioned above use a granular oxidizer, e.g., chlorine or bromine. In the absence of a granular oxidizer, there is seemingly no need to recognize that pleated, thin-strand polypropylene mesh (a common material for making pleated filter media) is attacked by concentrated oxidizers.
An improved filter cartridge overcoming some of the problems and shortcomings of earlier work in this field would be an important advance in the art.